Description of the Prior Art
It is known to manufacture metallic articles by superplastic forming and diffusion bonding metal workpieces. These metal workpieces include elementary metal, metal alloys and metal matrix composites. At least one of the metal workpieces must be capable of superplastic extensions.
The surfaces of the workpieces to be joined are cleaned, and at least one surface of one or more of the workpieces is coated in preselected areas with a material to prevent diffusion bonding. The workpieces are arranged in a stack and the edges of the workpieces are welded together, except where a first pipe is welded to the workpieces, to form an assembly. The assembly is placed in an autoclave and heated so as to "bake out" the binder from the material used to prevent diffusion bonding. The assembly is then evacuated via the pipe and the pipe is sealed. The sealed assembly is placed in a pressure vessel and is heated and pressed to diffusion bond the workpieces together to form an integral structure. Diffusion bonding occurs when two mating surfaces are pressed together under temperature, time and pressure conditions that allow atom interchange across the interface. The first pipe is removed and a second pipe is fitted to the diffusion bonded assembly in place of the first pipe assembly. The integral structure is located between appropriately shaped dies and is placed within an autoclave. The integral structure and dies are heated and pressurised fluid is supplied through the second pipe into the interior of the integral structure to cause at least one of the workpieces to be superplastically formed to produce an article matching the shape of the dies.
In the known method the welding of the pipe, for subsequently removing vaporised binder and for evacuating the assembly, to the workpieces is time consuming. The use of the pipe for removing vaporised binder from the assembly is also time consuming. Furthermore the assembly may contain air when it is heated to vaporise the binder and may result in oxidation of the surfaces of the workpieces which are subsequently to be diffusion bonded.